Method of treating lignocellulosic material or an expanded mineral to form a finished product

ABSTRACT

A method of preparing a starting material for the subsequent manufacture of a finished product such as a board, from a feedstock selected from the group consisting of a lignocellulosic material, exfoliated vermiculite, expanded perlite or a mixture of two or three thereof, includes the steps of providing the feedstock in the form of substantially dry finely divided lignocellulosic fibres or substantially dry finely divided exfoliated vermiculite or expanded perlite particles or a mixture thereof; mixing the feedstock with a suitable amount of a thermosetting resin in finely divided dry powder form and a suitable amount of the hydraulic binder in finely divided dry powder form; and optionally subjecting this starting material to suitable conditions of temperature and pressure to cause the thermosetting resin to set to form a cohesive product thereafter, there may be provided to the cohesive product, water in an amount sufficient for the hydration of the hydraulic binder so that the hydraulic binder sets to form the finished product.

BACKGROUND OF THE INVENTION

This invention relates to a method of preparing a starting material forthe subsequent manufacture of a finished product, from a feedstockcomprising substantially dry finely divided lignocellulosic fibres, orexfoliated vermiculite particles, or expanded perlite particles, and toa process of preparing a finished product therefrom.

Lignocellulosic composite board products, either in flat or shaped form,manufactured from chips, particles, fibres, veneers, flakes or strandsof natural fibrous plant materials such as agri fibres or wood, are wellknown and are currently made by a number of different methods. Suchproducts are commonly bound by formaldehyde condensation resins such asthe ureas, melamines and phenolics, or the polyureas or isocyanates.Despite the success of such lignocellulosic composite board products,there is always a need for new types of products, and in particular forproducts made from new types of feed material.

The material rejected in the mechanical cleaning of recovered paper isprobably in the region of ten million tons globally based on 1995figures and a 91% yield. The recycling of paper waste is rapidly fallingbehind demand for waste disposal. There is clearly a need for theutilisation of these materials but process difficulties have arisen. Oneis the presence of minerals in these materials, accounting for as high aproportion as 50% of the sludges and another is the difficulty inprocessing to make good quality products.

The present invention seeks to utilise the sludges, as well as otherfeedstocks such as medium density fibre, for the production of usefulproducts.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a methodof preparing a starting material for the subsequent manufacture of afinished product, from a feedstock selected from the group consisting ofa lignocellulosic material, exfoliated vermiculite, or expanded perlite,or a mixture of two or three thereof, which method includes the stepsof:

(1) providing the feedstock in the form of substantially dry finelydivided lignocellulosic fibres or substantially dry finely dividedexfoliated vermiculite particles or substantially dry finely dividedexpanded perlite particles, or a mixture of two or three thereof; and

(2) mixing the feedstock with:

(a) a suitable amount of a thermosetting resin in finely divided drypowder form, and

(b) a suitable amount of a hydraulic binder in finely divided dry powderform;

to give the starting material.

The method preferably includes the step of:

(3) subjecting the starting material of step (2) to suitable conditionsof temperature and pressure to cause the thermosetting resin to set toform a cohesive product.

According to a second aspect of the invention there is provided aprocess of preparing a finished product from a cohesive product producedby the method described above, which process includes the step of:

(A) providing to the cohesive product, water in an amount sufficient forthe hydration of the hydraulic binder so that the hydraulic binder setsto form the finished product.

By “finely divided lignocellulosic fibres” there is meant unifibres orbundles of a small number of unifibres of a lignocellulosic material. Inother words, the lignocellulosic material is broken down into singlefibres or bundles of a small number of fibres, rather than being in chipor particle form. The fibres have a length of from 0.5 mm to 12 mminclusive, preferably from 1 mm to 6 mm inclusive.

By “finely divided exfoliated vermiculite particles” there is meantexfoliated vermiculite in micron (0.5 mm and smaller), superfine (1 mmand smaller), fine (2 mm and smaller), medium (4 mm and smaller) andlarge (8 mm and smaller) particle size.

By “finely divided expanded perlite particles” there is meant expandedperlite or volcanic glass in particle sizes of from 5 microns to 2000microns diameter inclusive.

The lignocellulosic feedstock may already be in finely divided fibrousform.

However, in step (1) the lignocellulosic feedstock may be prepared frompellets or chips of a suitable material, by milling or abrading or thelike. In this case step (1) may precede or follow step (2).

The thermosetting resin is preferably a novolac phenol formaldehyderesin with a suitable catalyst.

The thermosetting resin is preferably used in an amount of 2% to 20%inclusive of the thermosetting resin by mass of the hydraulic binder,i.e the mass ratio of the thermosetting resin to the hydraulic binder isfrom 2:100 to 20:100.

The hydraulic binder is a substance which hydrates and sets incombination with water. The hydraulic binder is preferably selected fromthe group consisting of Portland Cement, high alumina cement, gypsumcement, calcium sulphate hemihydrate in either the alpha or beta form,magnesium oxychloride, magnesium oxysulphate, a calcium sulphoaluminatecement, an alkali silicate, and ground granulated blast furnace slag,and a mixture of any two or more of these binders.

The hydraulic binder is preferably used in an amount of 50% to 2000%inclusive of the hydraulic binder by mass of the feedstock, i.e the massratio of the hydraulic binder to the feedstock is from 1:2 to 20:1,preferably in a mass ratio of 10:1 to 5:1 for finished products withhigh densities, and preferably in a mass ratio of 5:1 to 1:1 forfinished products with low densities.

In addition to components (a) and (b), the feedstock may be mixed with:

(c) a suitable amount of a thermoplastic resin in finely dividedparticulate or fibrous form.

Further, in addition to components (a), (b) and optionally (c), thefeedstock may be mixed with:

(d) a suitable amount of a filler material selected from inorganic ormineral fibres, inorganic particles, synthetic fibres, and mixtures oftwo or more thereof.

In step (A) of the process, the water required for hydration of thehydraulic binder may be introduced into the cohesive product from anexternal source, for example as steam, or may be provided by one or moreof the components of the cohesive product, from which water is released,for example on heating.

DESCRIPTION OF EMBODIMENTS

The crux of the invention is that a feedstock, being substantially dryfinely divided lignocellulosic fibres, or substantially dry finelydivided exfoliated vermiculite or expanded perlite particles, or amixture of two or three thereof, is mixed with a thermosetting resin infinely divided dry powder form and with a hydraulic binder in finelydivided dry powder form to give a starting material. Thereafter thisstarting material is subjected to suitable conditions of temperature andpressure to cause the thermosetting resin to set to form a cohesiveproduct.

The provision of the feedstock in a finely divided fibrous orparticulate form is important to prevent particle separation in theformation of the starting material and subsequently the cohesiveproduct. A key feature of the cohesive product is that it may be formedfrom dry components that do not separate from one another duringformation of the cohesive product.

The feedstock may be lignocellulosic fibres.

A preferred lignocellulosic fibrous material is paper mill sludge, wastepaper or medium density fibre.

Paper mill sludge is a dewatered effluent of paper manufacture orrecycling.

A typical makeup of a paper mill sludge is a pH of 8.13, and a fibrepercentage of 14.4. An analysis of the sludge, utilising qualitativeX-ray emission scans, reveals a composition as follows: Ca 18%; K 0.23%;Cl 0.2%; P 0.15%; S 0.12%; Si 4.4%; Al 3%; Mg 0.8%; Na 0.17%; C 68% andFe 1.7%.

The hydrocarbon content as determined by the burn off method of thesludge is as follows:

INORGANIC ANALYSIS % LOI at 600° C. (indicative of total organics) 79,10% Ash at 900° C. 20,74 LOI = loss on ignition % Ash % Sample (m/m) (m/m)Calcium as CaO  8,28 1,72 Aluminium as Al₂O₃ 13,57 2,81 Magnesium as MgO 0,41 0,09 Iron as Fe₂O₃  0,43 0,09 Phosphates as PO₄3− NDetected ND(zero) Sulphates as SO₄2− 24,00 4,98 Acid insolubles 52,02 10,65 

ORGANIC ANALYSIS % Extractable Organic Matter 1,53 3000-2800 cm⁻¹ - C—H(aliphatic hydrocarbon) 1780-1650 cm⁻¹ - C—O (acid/ester absorption)1610 cm⁻¹ - C—H (aromatic group absorption) 1460 cm⁻¹ - CH₂(hydrocarbon) 1380 cm⁻¹ - CH₃ (hydrocarbon) 1250 cm⁻¹ - C—O (acid/esterabsorption) 1020, 750, 710 cm⁻¹ - C—H (aromatic group absorption)

The percentage consistency of such a sample is about 24.3% and the losson ignition of such a sample is about 27.9%.

The paper mill sludge, or waste paper which has been slushed to give a2% to 30% suspension in water, is cleaned, for example by centrifuging,to remove high and low density plastics, stone, sand and metal and othersuch impurities. The material is then passed to a clarifier from whichit emerges as a sludge or a 2% solids in water suspension. This sludgeis passed through a roller press to give approximately 20% solids inwater sludge, which is then typically fed through a screw press and apelletising screen to produce sludge pellets having a 30% to 60% solidspercentage. These pellets are then dried, typically in a rotary drier,to a moisture percentage from 0% to 15%, preferably in the range of from0% to 3%.

There pellets are then ready to use to form the feedstock for the methodof the invention.

The pelletising of the sludge is very important. It is essential toallow practicable drying, handling and mixing of the material with thethermosetting resin and the hydraulic binder.

In order to form the feedstock for the method of the invention, thepellets the paper mill sludge or waste paper must be milled. The millingmay be carried out prior to or after combination of the pellets with thethermosetting resin and the hydraulic binder.

The milling may be carried out in an attritor mill or a plate mill or astone mill, whereby two plates in close proximity to each other, eitherhorizontally or vertically, are moved at different speeds to each other,typically with one plate being stationary, although both plates maymove. The pellets are fed through the centre of the plates and are spunoutwardly by the centrifugal force. This causes the fibres in thepellets to separate without being reduced in length. All solidagglomerates are broken down into finely divided fibrous form.

The milling action also has the effect of introducing an electrostaticcharge into the lignocellulosic fibres which assists in adhering thethermosetting resin and the hydraulic binder thereto.

Electrostatic induction is an option during milling or blending toprevent sifting or powder separation. Electrostatic induction may beinduced by friction on the finely divided dry powder binder particlesboth organic and inorganic, before they are applied to the fibre in theblender or the fibres themselves may be electrostatically charged bypassing them through an electro magnetic field.

Another material for use as the feedstock of the invention is mediumdensity fibres (MDF). MDF is produced from soft woods or hard woods.Slab wood or round wood is converted into chips with a typical dimensionof about 20 mm in a chipping machine. The chips are then screened toremove undersized materials such as those below 5 mm, and oversizedmaterials such as those over 40 mm. The sized chips are then treated toremove adhering dirt or grit and are steamed for several minutes underpressure at a temperature of about 160° C. Thereafter the steamed chipsare forced into the narrow gap between the rotating discs of a refiner.An example of such a refiner is a Sund Defibrator. Individual fibres orfibre bundles are mechanically abraded from the surfaces of the steamsoftened chips. These then pass from the refiner to a dryer. Forexample, in a dryer the wet fibres, including some residual steam, arecombined with hot flue gases from a gas burner and the mixture thenpassed at high velocity along a flash drying tube. At the end of thetube the dried fibres are separated from the steam and the hot gases ina cyclone and are stored ready for use.

As stated above, the pellets of paper mill sludge or waste paper, or thefeed stock produced by milling of these pellets, or the MDF, is thenmixed with a thermosetting resin and with a hydraulic binder.

In the case of pellets of paper mill sludge or waste paper, the pelletsmay be mixed with the thermosetting resin and with the hydraulic binderprior to milling to assist in mixing of the various components.

Finely divided lignocellulosic fibres may also be derived from cerealstraw such as wheat, oats, barley or rice, fibrous material extractedfrom palm fronds, kapok, sisal, hemp, certain of the grass species,flax, and stalks of the cotton plant, fibres derived from husks from thecereal crops such as rice and wheat, and fibres extracted from groundnut shells and the like.

The feedstock may be exfoliated vermiculite particles.

Vermiculite belongs to the group of hydrated lamina industrial minerals,which are all aluminium-iron magnesium silicates, high in silica, andwhich propagate bonding in a cement matrix. They resemble a muscavite(mica) in appearance. When subjected to heat, vermiculite exfoliates dueto the inter lamina generation of steam. The pH is typically in theregion of 9, specific gravity 2.5, melting point 1315° C., sinteringtemperature 1260° C. and bulk densities are between 50 and 120 g/litre.The product exfoliated vermiculite is non corrosive, non combustible andnon abrasive. A typical particle size suitable for this invention is thegrade FNX by Micronised Products of South Africa, with a screen analysis−20 to 40% retained on a 2000 micron screen, 90 to 95% retained on a 710micron screen, or alternatively the grade SFX where 50 to 75% isretained on a 1000 micron screen, 20 to 35% retained on a 710 micronscreen and 0 to 10% retained on a 355 micron screen. Because exfoliatedvermiculite is compressible, densities of the final product may bereduced downward to as low as 850 kg/m³. Typical applications of thisspecification would be interior building boards for walls or ceilings,bound either with calcium sulphate hemihydrates or ordinary Portlandcement.

Perlite is a natural glass. It is an amorphous mineral consisting offused sodium potassium aluminium silicate. It occurs naturally as asilicacious volcanic rock. The distinguishing feature that sets perliteapart from other volcanic glasses is that when heated rapidly to above870° C., it expands to from four to twenty times its original volume asthe chemically combined water vaporises. This creates countless tinybubbles in the heat softened glassy particles. Typical chemical analysisof perlite indicates that silicon oxide percentage exceeds 70%,aluminium oxide exceeds 11% and metallic oxides make up virtually therest of the composition. Specific gravity is 2.3, softening point 870°C. to 1093° C. and fusion point 1260° C. to 1345° C. The preferredparticle size is from 200 to 2000 micron. An example is Genulite Grade M75 S by Chemserve Perlite (Pty) Ltd of South Africa.

The feedstock may also be a blend, in any proportion, of two or three ofthe materials described above.

For example, where a material is to be classified as a non-combustiblematerial, the organic percentage of the material should be below 7.5%.In this case, assuming that the thermosetting resin, which is regardedas an organic material, is present in an amount of 5%, then the maximumamount of lignocellulosic fibrous material which can be present is 2.5%.In this case, the remainder of the feedstock is comprised of exfoliatedvermiculite particles or expanded perlite particles or a mixturethereof.

The first component which is used with the feedstock is a thermosettingresin in finely divided dry powder form.

The thermosetting resin is preferably a novolac phenol formaldehyderesin, which is used with a suitable catalyst.

A novolac phenol formaldehyde resin is a resin in which the molar ratioof phenol to formaldehyde exceeds parity.

An example of a suitable catalyst for use with such a resin ishexamethylene tetramine. An example of a suitable novolac phenolformaldehyde resin and catalyst combination is a two stage resin with ahexamethylene tetramine content of between 6 and 14%, with a hot plategel time at 150° C. of between 40 and 120 seconds, with a flow in mm at125° C. of between 30 and 75 mm, and with a particle size sieve analysispercentage retained on a 200 mesh screen of a maximum of 2%. Examplesare the PRP resins of South Africa, code Varcum 7608 which may be usedas modifier for a slow curing phenolic system such as Varcum 3337. Amore rapid curing system i.e gel in 20-40 S, at 150° C., is preferredi.e PRP Code 7608.

The thermosetting resin is preferably used in an amount of 2% to 20%inclusive of the thermosetting resin by mass of the hydraulic binder,i.e in a mass ratio of the thermosetting resin to the hydraulic binderof from 2:100 to 20:100.

The second component is a hydraulic binder, i.e a substance whichhydrates and sets in combination with water.

The hydraulic binder is preferably chosen from the group comprisingPortland Cement, high alumina cement, gypsum cement, calcium sulphatehemihydrate either in the alpha or beta form, magnesium oxychloride,magnesium oxysulphate, a calcium sulphoaluminate cement, an alkalisilicate, such as sodium silicate, and a ground granulated blast furnaceslag or a combination of any two or more thereof.

The hydraulic binder is preferably used in an amount of 50% to 2000%inclusive of the hydraulic binder by mass of the feedstock, i.e a massratio of the hydraulic binder to the feedstock of from 1:2 to 7:1,preferably in a mass ratio of 10:1 to 5:1 for finished products withhigh densities, and preferably in a mass ratio of 5:1 to 1:1 forfinished products with low densities.

Other components may also be added into the mixture.

It has also been found that improvements may be achieved by mixing thefeedstock not only with a thermosetting resin and a hydraulic binder,but also with a suitable amount of a thermoplastic resin in finelydivided particulate or fibrous form.

The thermoplastic resin may be, for example, polypropylene, polyethyleneor polyvinyl chloride.

The thermoplastic resin has preferably been modified by irradiation orfluorination.

At temperatures in excess of 150° C., these particles or fibres of athermoplastic resin melt and flow to reinforce, and bind, and to provideeffectively a “platelet” inclusion in the matrix of the cohesive productformed.

Generally, the amount of thermoplastic resin added will be such so asnot to interfere with the water wicking propensity of the cohesiveproduct, necessary for subsequent rehydration of the hydraulic binder.

As stated above, the thermoplastic resin added has preferably beenmodified by irradiation or fluorination in order to propagatecross-linking and adhesion to the feedstock, as well as to the othercomponents of the starting material.

In the case of irradiation, the thickness of the thermoplastic film forfibre production may be between 5 and 3000 microns and the particle sizebetween 50 to 500 microns more preferably below 150 microns. Thethermoplastic fibres are made from a film or sheet through conversion ofa suitable thermoplastic polymeric starting material, modified byionising radiation prior to conversion to the film or sheet. Inaddition, the finely divided dry particles of thermoplastic polymer maybe modified with the same ionising radiation, in bags. The ionisingradiation employed can be produced either by a suitable radioactiveisotope, such as cobalt-60, or a suitable electron beam acceleratorwhich generates energetic electrons with an energy of 50 keV to 10 MeV.The absorbed radiation dose applied to the thermoplastic polymericstarting material may be of the order of 4 to 150 kGy and conventionalelectron beam accelerators or gamma irradiators can be employed for thispurpose.

In the case of fluorination, which is a less preferred method, theparticles of thermoplastic resin are fluorinated with fluorine gas,preferably diluted with either oxygen or nitrogen or other gas, up tothe level of 99%. Fluorine is a very strong oxidising agent and theprocess of fluorination induces the bonding of reactive groups to thepolymer, which in turn induces adhesion. In this case, much lowerpressing temperatures are desirable.

The inclusion of a thermoplastic resin propagates synergistic bindingwith the novolac resin or other thermosetting resin present. In additionthe thermoplastic resin is alkali resistant, contributes to toughness,reinforcement, flexural strength and resistance to impact in the finalproduct.

Another optional additive is a suitable amount of a filler materialselected from inorganic or mineral fibres such as rock wool, mineralwool, glass fibres and ceramic fibres; inorganic particles such assilica fume and fly ash; and synthetic fibres such as acrylic fibres,polyester fibres, acrylonitrile fibres, and the like.

These filler materials, when in particulate form, must have a surfacearea of 100 m² per kilogram or greater, and when in fibrous form, mustbe unifibres or bundles of a small number of unifibres.

A preferred filler material is silica fume. Silica fume has the capacityto react with free calcium hydroxide, forming calcium silicate hydrate.It accelerates the setting of the hydraulic binder. As a result of itsvery small particle size of 20,000 m²/kg, it minimises porosity in thefinished product, improves strength, minimises retardation by thesoluble substances in the lignocellulosic fibres, contributes to thecohesion of the cohesive product and minimises particle separation as afunction of its low bulk density. The silica fume, such as CSF-90 byAnglo Alpha Cement of South Africa, may be added in an amount of up to15% by mass on the mass of the hydraulic binder.

Another optional additive is a redispersable synthetic powder which isadded to modify the inorganic hydraulic binder. When a redispersablesynthetic powder is added, on subsequent water wetting of the cohesiveproduct, the powder redisperses and intimately wets the cohesiveproduct, imposing toughness, additional resistance to weathering, theability to breathe and proofness to water penetration.

Examples of these re-dispersible powders are the Vinnapas re-dispersiblepowders by Wacker Chemie. They are re-dispersible ethylene-vinyl acetateco polymer powders, examples being RE 526 Z and RE 530 Z or theterpolymer powder R1 538 Z, which has particularly high waterrepellence. These powder products improve adhesion between organic andinorganic components. Because of the presence of protective colloidsthey improve water retention during the hydration phase and theyminimise evaporation due to film formation at the surface. Flexuralstrength is improved, as is toughness. Addition levels are between 3 and10% more typically 5% on the weight of the binder used. Typical resintypes are vinyl acetate/ethylene co polymers with polyvinyl alcohol as aprotective colloid. The predominant particle sizes are 1 to 5 micron.Example of a homo polymer vinyl acetate dry powder for addition tocements are the Mowilith powders D and DS by Hoechst. A further exampleis Mowilith powder DM 200 P which is a fine particle size co polymer infinely divided dry powder form based on vinyl acetate and vinyl ester ofa long chain branched carboxylic acid. The Mowilith powders are alsosuitable for the modification of the composite board product properties.

Auxiliary acceleration of binding of the hydraulic binders may beprovided by water donors such as the hydrates or hemi hydrates ofcalcium sulphate, or certain of the aluminium trihydrates or the like,which give off chemically bound water at elevated temperatures duringthe forming of the product. In addition catalytic or synergistic binderaids may be included such as calcium oxide to speed the set of sodiumsilicate or sodium silicate cement blends, and fly ash or silica fumeacting as a pozzolanic binders, or finely ground limestone, in thelatter two cases propagating rapid hydration by crystal “seeding”.

There may also be incorporated other additives, such as for example afire retardant or fire inhibitor, a bactericidal agent, a fungicide, aninsecticide, an ultra violet light stabiliser or absorber, an antioxidant, a scent or a deodoriser.

Lignocellulosic water soluble extractives may inhibit the setting ofsome hydraulic binders, particularly Portland cement. It is thought thatinhibition is a function of the “sheathing” of available calcium ions,retarding the growth of calcium silicate hydrates. It is water solublesugars, water soluble higher carbohydrates such as hemicellulose, andinsoluble carbohydrates that solubilise under the influence of the highalkalinity of Portland cement, that are chiefly responsible. Ligninshave no inhibitory effect. Therefore the choice of lignocellulosic fibrecan be important. Minimising or eliminating the inhibiting effects ofwater soluble lignocellulosic extractives may be achieved by thefollowing:

1 The addition of soluble inorganic salts as accelerators, particularlythe chlorides of zinc, iron, magnesium, aluminium or calcium, butparticularly calcium in the form of calcium chloride. These are added inthe proportions of 1% to 7% by mass of the starting material but morepreferably in the range of 2% to 5%. Calcium chloride promotes anincreased amount of calcium ions in the matrix. The draw back ofchlorides being potentially highly corrosive, is not as significant in acomposite not containing metal reinforcement.

2 The inclusion of a silica fume as a superpozzalan accelerating theformation of calcium silicate hydrate by reacting with the calciumhydroxide formed during early hydration reactions.

3 Impregnating water into the formed composite while it is still hotfrom the press, but below 100° C., in order to accelerate the chemicalhydration reaction.

4 The inclusion of quick reaction chemicals such as aluminium sulphateto accelerate hydration reactions.

When all the components have been mixed, the starting material may besubjected to suitable conditions of temperature and pressure to causethe thermosetting resin to set to form a cohesive product.

For example, the mixture may be placed in a suitable press or mould andthen subjected to suitable conditions of pressure and temperature toallow the resin present to polymerise or set.

More specifically for example, the mixture may be compressed and heatedin a suitable press or mould at temperatures from 125° C. to 255° C.inclusive, preferably from 140° C. to 225° C. inclusive, and pressuresof from 5 to 70 kg/cm² (0,49-6,9 MPa) inclusive.

This results in a cohesive product which may then be stored for anylength of time before being formed into a finished product.

As an alternative, the mixture from step (2) may be stored for furtherprocessing.

The cohesive product so produced as described above may then be utilisedin a process for preparing a finished product. According to thisprocess, there is provided to the cohesive product, water in an amountsufficient for the hydration of the hydraulic binder so that thehydraulic binder sets to form the finished product.

For example, in the pressing step, steam may be injected into thecohesive product through apertures in the press plates or in the mould,which steam provides the water for hydration of the hydraulic binder toform the finished product.

Alternatively, after pressing, water may be applied to the cohesiveproduct to allow the penetration of a suitable quantity thereof toprovide for complete hydration of the hydraulic binder to form thefinished product.

As a further alternative, the cohesive product may be placed in anautoclave and then subjected to a vacuum for typically 15 minutes.Thereafter water is introduced into the autoclave until it is full andthen the water is subjected to a pressure of typically 6 bar for 20minutes. Thereafter the water is expelled by compressed air. This methodallows the water uptake of the cohesive product to be controlled withinnarrow limits, typically in the range of 19 to 28% of the mass of thecohesive product.

As a further alternative, the water necessary for hydration may beprovided by a component or components of the cohesive product so that,for example, on heating, this water is released and is utilised by thehydraulic binder to hydrate and set.

Auxiliary binders in liquid form may be blended with the water forhydration chosen from the group comprising of:

(i) a sodium silicate solution

(ii) a polymer dispersion such as a polyvinyl acetate or acrylic.

(iii) a polyvinyl alcohol solution, such as the partially hydrolysed lowviscosity specifications, i.e a 3% solution of Mowiol 4/88 by Hoechst.

(iv) a magnesium oxide solution

(v) a calcium oxide solution

When the hydraulic binder is a magnesium oxide, then the water mayinclude hydrochloric acid so that the magnesium oxide is converted to amagnesium oxychloride binder.

The finished product may be for example a board which may be either flator corrugated or otherwise shaped or a profile.

The invention therefore provides a means of converting paper mill sludgeor mixed common paper waste or MDF or other suitable fibrous orparticulate material, into a value added product suitable for use in thefurniture or building industry. The hydraulic binders such as Portlandcement impose upon the product suitable resistance to water swelling,resistance to weathering and to fire, and make the board suitable as anexterior exposed building product. Where calcium sulphates are used,adequate behaviour in fire, appropriate cohesive strength and excellentfinishing properties are imposed, though lower process temperatures arerequired. Moreover when either Portland cement or calcium sulphate isused the resulting board product is less brittle than the conventionalcementitious or gypsum board products, and cuts and works or machinesmore easily and has excellent finishing properties as a result of thereinforcing element of the finely divided lignocellulosic fibre, theauxiliary binding of the novolac and the inorganic binding contributionof the hydraulic binder. Synergy between the hydraulic binders may bemade use of. For example, blending of a calcium sulphate hemihydratewith a Portland cement may rapidly accelerate the setting of the bindersand contribute to better properties in the final product.

Additional hydrophobisation of the finished product when boundprincipally by inorganic binders, particularly Portland cement, isimposed by including in the water for hydration, added after productforming, of silicone micro emulsion concentrate dispersed in water atthe level of from 0.2 to 8%, more generally in the range of 1 to 3%,thereby forming silicone mesophases with a particle size in the submicroscopic range of 10 to 80 nm. The silicone micro emulsions or SMCshave great alkali stability and good penetration properties. Examplesare Wacker BS1306, Wacker BS1000 and Wacker 1311. Wacker BS 1306 is asolvent free water miscible emulsion of a polysiloxane modified withfunctional silicone resin. It imposes water resistance, water repellencyand water vapour permeability.

It is to be noted that by varying the type and quantity of feedstockused to make the starting material, and then the cohesive product andthus the finished product, the density of the finished product may bevaried considerably. For example, by using exfoliated vermiculite as thefeedstock, either alone or in part, densities may be reduced 700 kg/m³.At the other end of the scale, a finished product with a density of 2000kg/m³ may be prepared, which product is suitable as a floor or wall tileor roof tile.

It is also possible to make a finished product consisting of two or morelayers or horizons. For example, it is possible to make a finishedproduct where the two outer layers of the product comprise exfoliatedvermiculite with hydraulic binder and thermosetting resin, and where theinner layer is formed from a lignocellulosic fibrous material, hydraulicbinder and thermosetting resin. This provides a finished product with nolignocellulosic component exposed. Instead, the outer layers containexfoliated vermiculite which is stable and does not expand or contracton water wetting, and is inert and fireproof.

Other advantages of the method of the invention are that the cohesiveproduct may be cut to size and machined, prior to preparation of thefinished product. All waste resulting from the sizing and machining maybe returned to the beginning of the method for reuse. This is notpossible with products made by the conventional wet methods. Inaddition, the method of the invention is generally quicker and cheaperthan conventional wet methods of manufacture of similar products.

EXAMPLE 1

An example of an exterior building board made by the method of theinvention will now be given:

1 100 kg of paper mill sludge is pelletized to pellet sizes ofapproximately 4mm diameter, and these are dried to 10% water content.

2 The product of step 1 is milled in an attritor stone mill.

3 180 kg of ordinary Portland cement is blended with 35 kg of sodiumsilicate SP33 by Silicate & Chemical Industries of South Africa withSiO₂ to Na₂O weight ratio of 3,3 to 1, and with 7 kg of Novolac ResinCode 3337 by PRP with a hexamethylene tetramine percentage of 6,3 to6,8%.

4 The product of step (3) is blended with that of step (2)

5 The product of step (4) is laid up on a caulk plate at 13,50 kg/m².

6 The product of step (5) is pressed to a thickness of 10 mm at apressure of 37 kg/cm² (3,63 MPa) and temperature of 180° C. for 5minutes to form a board.

7 The board is now irrigated with a 1½% solution of Mowiol (by Hoechst)code 4/88 polyvinyl alcohol in water solution at the rate of 1 kg perside, a total of 2 kg/m², left until full cement cure is achieved.However, immediately on water wetting, the sodium silicate reacts withuncombined calcium present in the cement to form insoluble calciumsilicate thus blocking the pores and hardening the surface. This rendersthe cementitous composite waterproof, reduces dusting, increasesabrasion resistance, increases resistance to acid attack, renders thecement board oil proof and propagates the very rapid, almostinstantaneous set of hydraulic binders present.

Auxiliary binding is provided by the polyvinyl alcohol but its principalfunction is to beneficiate the reinforcing and integrity of thelignocellulosic fibres.

EXAMPLE 2

An example of a roof tile manufactured by the method and process of theinvention is given below. The following ingredients are mixed as acompletely dry feedstock combination and laid up in a uniform mat beforeentry into the press:

250 kg  Catalysed ground blast furnace slag 250 kg  Rapid hardeningPortland cement 75 kg Un-densified silica fume 50 kg Specially milledcoconut palm tree leaf fibre 200 kg  Micron grade particle sizeexfoliated vermiculite 50 kg Mica 70 kg Novolac dry powder resincontaining hexamethylene tetramine catalyst  7 kg Calcium chloride asaccelerator

This is pressed at 45 bar (4.5 MPa) at 180° C. to form a cohesiveproduct. Roof tiles are produced typically in a carousel configuration.After pressing, they are trimmed, stacked, placed in an autoclave, andoptionally subjected to a vacuum (15 KPa) for 15 minutes, after whichwater may be introduced and subjected to a pressure of 6 bar (0.6 MPa)for 20 minutes. The absorption of water by the pressed roof tiles is anaverage 23% by mass of the dry roof tile before water impregnation.Cement hydration is allowed to go to completion. The tiles may then bedried, decorated and shipped. The advantage is that they may be half thethickness and half the weight of conventional concrete roof tiles. Thefinal density of the product is of the order of 1900 kg/m³.

EXAMPLE 3

A further example of a light weight non-combustible cementitious boardfor building applications such as sheathing is made of the following:

60 kg Milled paper mill sludge 750 kg  Micron grade exfoliatedvermiculite 1200 kg  Rapid hardening Portland cement  7 kg 10 mmPolyethylene fibre 90 kg Novolac dry powder phenol formaldehyde resincontaining hexamethylene tetramine catalyst.

This composite is mixed, laid up in a mat of uniform bulk density and ispressed at a temperature of 200° C. for 10 seconds per mm thickness at apressure of 4 MPa to yield a cohesive product. After the impregnation ofwater by vacuum and pressure in an autoclave and after the cement hasbeen fully hydrated, the product is dried to give a board which has afinal dry density of 825 kg/m³. The boards are sanded to a smooth finishfor ease of painting.

What is claimed is:
 1. A method of preparing a cohesive product containing a hydraulic binder, for the subsequent manufacture of a finished product by hydration of the hydraulic binder in the cohesive product, from a feedstock selected from the group consisting of a lignocellulosic material, exfoliated vermiculite, expanded perlite, and a mixture of two or three thereof, which method includes the steps of: (1) providing the feedstock in the form of substantially dry finely divided linocellulosic fibres, or substantially dry finely divided exfoliated vermiculite particles, or substantially dry finely divided expanded perlite particles, or a mixture of two or three thereof; (2) mixing the feedstock with: a) a suitable amount of a thermosetting resin in finely divided dry powder form, and b) a suitable amount of hydraulic binder in finely divided dry powder form; to give a dry starting material; and (3) forming the dry starting material of step (2) while subjecting it to suitable conditions of temperature and pressure to cause the thermosetting resin to set to form the cohesive product.
 2. A method according to claim 1 wherein the mass ratio of the hydraulic binder to the feedstock is from 1:2 to 20:1.
 3. A method according to claim 1 or claim 2 wherein the mass ratio of the thermosetting resin to the hydraulic binder is from 2:100 to 20:100.
 4. A method according to claim 1 wherein the thermosetting resin is a novolac phenol formaldehyde resin which is used with a catalyst.
 5. A method according to claim 1 wherein the hydraulic binder is selected from the group consisting of Portland cement, high alumina cement, gypsum cement, calcium sulphate hemihydrate in either the alpha or beta form, magnesium oxychloride, magnesium oxysulphate, a calcium sulphoaluminate cement, a alkali silicate, ground granulated blast furnace slag, and a mixture of two or more thereof.
 6. A method according to claim 1 wherein in step (1) pellets or chips of a suitable material are milled prior to or after step (2) to reduce the pellets or chips to a feedstock comprising substantially dry finely divided lionocellulosic fibres.
 7. A method according to claim 1 wherein in step (2) the feedstock is mixed with: (c) a suitable amount of a thermoplastic resin in finely divided particulate or fibrous form.
 8. A method according to claim 1 wherein in step (2) the feedstock is mixed with: (d) a suitable amount of filler material selected from inorganic or mineral fibres inorganic panicles, synthetic fibres, and mixtures of two or more thereof.
 9. A method according to claim 1 wherein in step (3) the starting material of step (2) is subjected to a temperature of from 125° C. to 255° C. inclusive and a pressure of from 0,49 to 6,9 MPa inclusive.
 10. A process of preparing a finished product from a cohesive product produced by the method of claim 1, which process includes the step of: (A) providing to the cohesive product, water in an amount sufficient for the hydration of the hydraulic binder so that the hydraulic binder sets to form the finished product.
 11. A process according to claim 10 wherein in step (A) water is applied to the cohesive product to allow the penetration of a suitable quantity thereof to provide for complete hydration of the hydraulic binder to form the finished product.
 12. A process according to claim 10 wherein in step (A) the water necessary for hydration is provided by a component or components of the cohesive product so that on heating the water is released and is utilised by the hydraulic binder to hydrate and set. 